Spreadplayers Command

The spreadplayers command is a great command, however there is one limitation that I have come across. I am trying to set up the spreadplayers command to move some entities under X blocks above a different entity. I am trying to have it spread entities under a roof without knowing the Y coordinate of the roof, only knowing its relation to a different entity. Is there a way to do this with the commands provided or can someone code that functionality into Minecraft?